Narrow-linewidth single-mode vertical-cavity surface-emitting laser

Abstract

A coupled-cavity vertical-cavity surface-emitting laser (VCSEL) is disclosed. The coupled-cavity VCSEL includes a passive cavity and an additional distributed Bragg Reflector (DBR) not found in conventional VCSELs, all in a monolithic device. By including these two elements, the photon lifetime may be increased by a factor of approximately ten, leading to a reduction in the laser linewidth by a factor of approximately 100 compared to conventional VCSELs. The two additional elements also serve to ensure single-mode operation of the coupled-cavity VCSEL.

The invention claimed is: 
     
       1. A coupled-cavity vertical-cavity surface-emitting laser comprising:
 a bottom reflector adapted to be very highly reflective at an operating wavelength; 
 a passive cavity formed on the bottom reflector, the passive cavity having a thickness substantially equal to an integer multiple of one half of the operating wavelength in the passive cavity; 
 a middle reflector formed on the passive cavity, the middle reflector adapted to be moderately reflective at the operating wavelength; 
 an active region formed on the middle reflector, the active region adapted to provide optical gain at the operating wavelength; and 
 a top reflector formed on the active region, the top reflector adapted to be highly reflective at the operating wavelength, the top reflector adapted to transmit an optical output when the coupled-cavity vertical-cavity surface-emitting laser is operating. 
 
     
     
       2. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein the bottom reflector is a distributed Bragg reflector and has a reflectivity at the operating wavelength of at least approximately 99.9%. 
     
     
       3. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein the middle reflector is a distributed Bragg reflector, and has a reflectivity at the operating wavelength between approximately 15% and approximately 30%. 
     
     
       4. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein the top reflector is a distributed Bragg reflector, and has a reflectivity at the operating wavelength between approximately 99.0% and approximately 99.7%. 
     
     
       5. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein each of at least the middle reflector, the active region, and the top reflector comprises at least one of II-VI semiconductor material, III-V semiconductor material, and IV semiconductor material. 
     
     
       6. The coupled-cavity vertical-cavity surface-emitting laser of  claim 5 , wherein each of the bottom reflector and the passive cavity comprises at least one of II-VI semiconductor material, III-V semiconductor material, and IV semiconductor material. 
     
     
       7. The coupled-cavity vertical-cavity surface-emitting laser of  claim 6 , wherein at least a portion of the passive cavity and the middle reflector are doped a first type and the top reflector is doped a second, opposite type. 
     
     
       8. The coupled-cavity vertical-cavity surface-emitting laser of  claim 5 , wherein each of the bottom reflector and the passive cavity comprises at least one dielectric material. 
     
     
       9. The coupled-cavity vertical-cavity surface-emitting laser of  claim 5 , wherein the semiconductor materials used to form each of the middle reflector, the active region, and the top reflector are substantially lattice matched. 
     
     
       10. The coupled-cavity vertical-cavity surface-emitting laser of  claim 5 , wherein at least a portion of the middle reflector is doped a first type and the top reflector is doped a second, opposite type. 
     
     
       11. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein the integer multiple is at least four. 
     
     
       12. The coupled-cavity vertical-cavity surface-emitting laser of  claim 11 , wherein the integer multiple is at least eight. 
     
     
       13. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , further comprising:
 a bottom contact in electrical contact with the active region; and 
 a top contact in electrical contact with the active region; 
 wherein the bottom contact and the top contact are adapted to provide a drive current to the active region. 
 
     
     
       14. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , further comprising a current aperture adapted to limit a flow of a drive current in the active region. 
     
     
       15. The coupled-cavity vertical-cavity surface-emitting laser of  claim 14 , wherein the current aperture is formed in a perimeter portion of the top reflector adjacent the active region. 
     
     
       16. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , further comprising:
 a bottom doped layer located between the middle reflector and the active region; and 
 a top doped layer located between the active region and the top reflector; 
 wherein the bottom doped layer and the top doped layer are adapted to provide a drive current to the active region. 
 
     
     
       17. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 ,
 wherein the middle reflector includes:
 a first lower, undoped plurality of layers; 
 a first middle, doped single composition layer formed on the first lower, undoped plurality of layers; and 
 a first upper, doped plurality of layers formed on the first middle, doped single composition layer. 
 
 
     
     
       18. The coupled-cavity vertical-cavity surface-emitting laser of  claim 17 ,
 wherein the top reflector includes:
 a second lower, doped plurality of layers; 
 a second middle, doped single composition layer formed on the second lower, doped plurality of layers; and 
 a second upper, undoped plurality of layers formed on the second middle, doped single composition layer. 
 
 
     
     
       19. The coupled-cavity vertical-cavity surface-emitting laser of  claim 18 , wherein the middle reflector and the top reflector are adapted to provide a drive current to the active region. 
     
     
       20. The coupled-cavity vertical-cavity surface-emitting laser of  claim 1 , wherein the passive cavity has an index of refraction greater than approximately 1.4.